The present invention relates to a process for the preparation of peroxides and more especially to a process for the preparation of bivalent metal peroxides.
Peroxides of bivalent metals are being used increasingly for technological applications. Thus, for example, alkaline earth metal peroxides are used for medical and pharmacological purposes and in cosmetics. Recently, CaO.sub.2 has been growing in importance, as it serves to improve the growth of cultivated plants. In sewage treatment, the potential of the slow release of oxygen by peroxide compounds is being utilized. Metal peroxides are also used in the technical fields of vulcanizing and welding.
Peroxides of bivalent metals are generally prepared by producing peroxide-containing reaction mixtures from aqueous solutions or dilute suspensions of their salts, oxides or hydroxides by means of conversion with aqueous hydrogen peroxide solutions, centrifuging or filtering the mixture and drying them on rack or tray drying apparatus. The dry substances are ground and possibly screened in a conventional manner.
A process for the preparation of CaO.sub.2 is known from German Offenlegungsschift No. 15 42 642, wherein a highly dilute solution of hydrogen peroxide is reacted with an excess of calcium hydroxide at temperatures below 30.degree. C. to produce calcium peroxide-octahydrate, which then is converted in an additional drying stage into the anhydrous peroxide.
All of these known processes have numerous disadvantages. They are costly, because of the need of separating the mother liquor by centrifuging and the grinding of the product dried on racks or trays. Furthermore, the economy of the process is limited, because significant losses of peroxide are generated by decomposition of hydrogen peroxide as the result of the large volumes of mother liquor caused by the relatively dilute suspensions, and in the drying process, as the result of long retention times.
Furthermore, because of the strong dilution of the reaction mixture, large volumes of water must be transported unnecessarily and they must be removed in an energy-intensive drying stage. In addition, supplemental control devices are required for temperature control as well as additional process stages for the removal of the excess calcium hydroxide. A further disadvantage is a certain lack of homogeneity of the end product, resulting from decomposition during drying and the subsequent grinding process.